The Roman Polyspastos

The Roman Polyspastos was a compound-pulley crane powered by human labor. By combining multiple pulleys, ropes, and winches (or treadwheels), it allowed a small crew to lift heavy loads of 3,000 to 6,000 kg. This engineering leap propelled the construction of monumental temples, aqueducts, and amphitheaters. The simplest 3-pulley crane (the trispastos) could lift about 150 kg with one person. The polyspastos, with its multiple pulleys, could lift 3,000 kg when operated by four men.

To increase mechanical advantage, Romans often replaced the traditional hand-cranked winch with a large wooden treadwheel. Workers walked inside the wheel, doubling the maximum lifting capacity to 6,000 kg without adding more men.

The Haterii relief is a late 1st-century AD stone relief found on the Tomb of the Haterii. It shows a polyspastos at work. The ancient machine allowed the Haterii family to erect massive temple-style tombs, multi-storied tenements, and grand imperial monuments during the Flavian dynasty. While capable of lifting stones up to 6 tonnes, Romans used a separate method for even heavier loads. They built wooden lifting towers which housed specialized pulleys, winches, and human-powered treadwheels to lift weights that could exceed 50 tons.